Lenticular images typically employ cylindrical lens arrays which have been extruded and cut into standard size sheets. In current practice using conventional techniques, these sheets are usually reverse-printed on their flat, unlenticulated side with a specially prepared interlaced image. Because the lens arrays allow the image to vary with the angle of view, lenticular images can be given diverse properties of apparent depth and animation. These properties have long been found to be highly effective in advertising, marketing, and promotion. In addition, such qualities are perceived as having a degree of interest and value apart from the initial visual encounter.
Lenticular printing is a multi-step process consisting of creating a specially prepared lenticular image from at least two existing images, and then combining it with a lenticular lens sheet. Depending on the specifics of the image preparation, this process can be used to create various frames of animation (for a motion effect), offsetting the various layers at different increments or establishing differing angular views (for a 3D effect), progressively scaling a chosen locus within an image (for a zooming effect), or simply to show a set of alternate images which can appear to transform into each other. Once the various images are collected, they are processed into differing frame files, and then digitally combined into a single final file in a process called interlacing.
In this operation, each image is arranged into strips, which are then interlaced with one or more similarly divided images. Originally this integration was performed optomechanically, however, the interlacing process can now be performed digitally with great accuracy and repeatability.
These interlaced images are often printed on the back of a piece of plastic which has an array of lenses formed in the opposite side. These lenses are usually cylindrical in geometry, but elliptical and parabolic profiles have also been put in practice. Extrusion is the most common method for manufacturing the lens sheet, but film casting, embossing, and molding are also known. Historical practices are also known in which the lenses are formed using a layer of gelatin, lacquer, curable polymer, or other transparent material directly upon interlaced printed imagery. Lenses can be radial in geometry as well as linear, although radial lens elements are less often practiced. Methods of producing periodic image effects, such as moiré patterns or repeating icons, are understood to be attainable without precise interlacing. These optical products nevertheless share the conceptual and structural foundation of lenticular prints.
Offset printing directly to the flat rear surface of the polymer lenticular sheet is the most common current practice for volume production. However, images can nevertheless be printed independently on paper or white polymer film, and subsequently bonded to the plastic lens sheet. This practice is commonly followed when special formats or short runs are specified.
In any case, the alignment of the lenses with their corresponding interlaced image fields is critical to the success of the chosen optical effect. In offset printing, this alignment is achieved in elaborate trial set-up and make-ready operations. However, when the images are to be preprinted and laminated, the alignment of the image sheet and lens sheet in each instance is usually incumbent on a skilled operator. Because this critical step is time-consuming, error-prone, and therefore often cost-prohibitive, short runs and individual pictures have been largely excluded from the lenticular trade.